Real-time clock battery life calculation

Battery Capacity Consumption

When Vcc is being held by the external power supply within
its specified range, the current drawn from the battery is zero.
When Vcc falls below the Battery Back-up Switchover Voltage (Vso),
the device goes into battery back-up mode, and draws all its current
from the battery.

The Vcc duty cycle represents the proportion of time, expressed
as a percentage, that the device is supplied with power from the
external supply, and hence not drawing current from the battery.

Calculating Battery Lifetime

Capacity consumption is simply calculated by:

Battery Capacity

8760 * (1) * Ibat

where:
 Battery Capacity is measured in ampere-hours;
 8760 is the constant for the number of hours there are
in a year;
 Vcc Duty Cycle is measured as a percentage (100% in this
case); and
 Ibat is measured in amperes.
To calculate the typical and worse case data retention lifetimes,
select the Serial RTC Device and then enter the battery capacity
of your choice in the form below (in mAh), and click on Calculate.
The calculated typical and worst case Battery Life (@25°C)
in years will be then be displayed.

Device:

Enter Battery Capacity(1) (mAh):

Battery Lifetime(2) (in Years @ 25°C)

Calculated Typical:

Calculated Worst
Case:

Note 1:

M4T28-BR12SH = 48mAh;
M4T32-BR12SH = 120mAh

Note 2:

Excluding Iout2 and/or Tamper Current for those devices
with Vout or Tamper Inputs.